JP2009176602A - Battery system and automobile - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery system capable of restraining increase of internal resistance of a lithium ion secondary battery during a standstill period of the lithium ion secondary battery, and to provide an automobile. <P>SOLUTION: The battery system 6 comprises the lithium ion secondary battery 100, and a temperature control means (microcomputer 30) for controlling temperature of the lithium ion secondary battery 100. The temperature control means (microcomputer 30) performs temperature control for maintaining temperature of the lithium ion secondary battery 100 at a designated upper-limit temperature value or below during a standstill period, wherein the lithium ion secondary battery 100 is standstill. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a battery system including a lithium ion secondary battery and an automobile including the battery system.

  Secondary batteries such as lithium ion secondary batteries and nickel metal hydride secondary batteries are attracting attention as power sources for portable devices and power sources for electric vehicles and hybrid vehicles. At present, various battery systems including secondary batteries have been proposed (see, for example, Patent Document 1).

JP 2004-327385 A

  Patent Document 1 discloses a battery system that performs refresh charge / discharge when the temperature difference between the single cells constituting the battery pack exceeds a certain value during charge / discharge of the battery pack. It is described that by performing refresh charging / discharging, inactivation of the nickel-metal hydride storage battery can be eliminated and the battery capacity can be made uniform, so that the battery can be used effectively.

  By the way, in a lithium ion secondary battery, if a resting state (state in which charging / discharging is not performed) continues for a long period of time (for example, 10 hours or more), the internal resistance increases. The increase in the internal resistance of the lithium ion secondary battery during the suspension period tends to increase as the battery temperature during the suspension period increases (particularly 40 ° C. or more). In such a lithium ion secondary battery whose internal resistance has greatly increased, sufficient output characteristics may not be obtained. In particular, when used as a driving power source for a hybrid vehicle or an electric vehicle that requires a large output, there is a possibility that an output necessary for traveling (especially at the start) cannot be obtained.

However, the technique disclosed in Patent Document 1 cannot suppress an increase in internal resistance of the lithium ion secondary battery during the rest period.
The present invention has been made in view of such a situation, and a battery system capable of suppressing an increase in internal resistance of a lithium ion secondary battery during an idle period of the lithium ion secondary battery, and an automobile. The purpose is to provide.

  The solution is a battery system comprising a lithium ion secondary battery and a temperature control means for controlling the temperature of the lithium ion secondary battery, wherein the temperature control means has the lithium ion secondary battery suspended. It is a battery system which performs control which maintains the temperature of the said lithium ion secondary battery below a predetermined | prescribed upper limit temperature value during the idle period which is a state.

In the battery system of the present invention, control is performed to keep the temperature of the lithium ion secondary battery at a predetermined upper limit temperature value (for example, 40 ° C.) or less during a pause period in which the lithium ion secondary battery is in a pause state. Thus, by keeping the battery temperature at a temperature equal to or lower than the upper limit temperature value during the rest period, it is possible to suppress an increase in the internal resistance of the lithium ion secondary battery during the rest period.
The “resting state” refers to a state where the lithium ion secondary battery is not being charged / discharged. However, this includes not only a state in which no current flows through the lithium ion secondary battery but also a state in which a minute current of several tens of μA or less flows.

  Furthermore, in the battery system described above, it is preferable that the predetermined upper limit temperature value is 40 ° C.

When a lithium ion secondary battery is in a rest state for a long period (for example, 10 hours) in a state where the temperature of the lithium ion secondary battery is higher than 40 ° C., the internal resistance greatly increases.
On the other hand, in the battery system of the present invention, the predetermined upper limit temperature value is 40 ° C. That is, temperature control is performed to keep the temperature of the lithium ion secondary battery at 40 ° C. or lower during the pause period in which the lithium ion secondary battery is in a pause state. Thereby, since the temperature of a lithium ion secondary battery can be maintained at 40 degrees C or less, the raise of the internal resistance of a lithium ion secondary battery can be suppressed further.

  Furthermore, in any one of the battery systems described above, when the temperature of the lithium ion secondary battery has reached a first specified value lower than the upper limit temperature value, the lithium ion secondary battery It is preferable to use a battery system that performs control for starting cooling of the battery.

When the temperature of the lithium ion secondary battery reaches the first specified value lower than the upper limit temperature value, the temperature of the lithium ion secondary battery is appropriately increased to the upper limit by starting cooling of the lithium ion secondary battery. It can be kept below the temperature value. The first specified value is preferably set to a temperature that is 1 to 5 ° C. lower than the upper limit temperature value.
Specifically, for example, when the upper limit temperature value of the lithium ion secondary battery is 40 ° C., the first specified value is set to a temperature value within a range of 35 ° C. to 39 ° C. (eg, 36 ° C.). Then, when the battery temperature rises to a first specified value (for example, 36 ° C.), the cooling device (cooling fan or the like) is operated to cool the lithium ion secondary battery. Thereby, the temperature of a lithium ion secondary battery can be kept at 40 degrees C or less appropriately.

  Furthermore, in any of the battery systems described above, the lithium ion secondary battery may be a battery system that serves as an operating power source for the temperature control means.

  In the battery system of the present invention, a lithium ion secondary battery that is a temperature control target is used as a power source for operating the temperature control means. For this reason, it is not necessary to provide a separate power source for the temperature control means in addition to the lithium ion secondary battery that is a temperature control target, and space saving and low cost are achieved.

  Another solution is an automobile provided with any one of the battery systems described above, wherein the lithium ion secondary battery is used as a power source for driving the automobile.

A large output is required for a lithium ion secondary battery mounted as a driving power source for a hybrid vehicle or an electric vehicle (especially when starting a vehicle).
By the way, for example, if a car is not used (parked) for a long period of time (for example, 10 hours or more) and a lithium ion secondary battery mounted as a driving power source continues during that period, The internal resistance of the secondary battery will increase. In particular, if the lithium ion secondary battery continues to be idle for a long period of time when the battery temperature exceeds 40 ° C., the internal resistance of the lithium ion secondary battery is greatly increased. As described above, when the internal resistance of the lithium ion secondary battery mounted as a driving power source for the automobile is greatly increased, there is a possibility that an output necessary for traveling (particularly at the start) of the automobile cannot be obtained.

  On the other hand, the automobile of the present invention includes the above-described battery system, and uses a lithium ion secondary battery included in the battery system as a power source for driving the automobile. For this reason, the battery temperature can be kept at a temperature equal to or lower than the upper limit temperature value during the suspension period, and an increase in the internal resistance of the lithium ion secondary battery that is the driving power source can be suppressed. Thereby, in the automobile of the present invention, good running performance (particularly, running performance at the start) can be exhibited.

(Embodiment)
Next, embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the automobile 1 according to the present embodiment includes a vehicle body 2, an engine 3, a front motor 4, a rear motor 5, a battery system 6, a cable 7, and a generator 9, and the engine 3 and the front motor 4. And a hybrid vehicle driven in combination with the rear motor 5. Specifically, the automobile 1 includes the battery system 6 (specifically, the assembled battery 10 of the battery system 6, see FIG. 2) as a power source for driving the front motor 4 and the rear motor 5, using known means. And the front motor 4 and the rear motor 5 are configured to be able to travel.

  Among these, the battery system 6 is attached to the vehicle body 2 of the automobile 1 and is connected to the front motor 4 and the rear motor 5 by a cable 7. As shown in FIG. 2, the battery system 6 includes an assembled battery 10 in which a plurality of lithium ion secondary batteries 100 (unit cells) are electrically connected to each other in series, a current detection unit 60, and a microcomputer 30. ing. The microcomputer 30 has a ROM 31, a CPU 32, a RAM 33, and the like. The current detection means 60 detects the current value I flowing through the lithium ion secondary battery 100 constituting the assembled battery 10.

As shown in FIG. 2, the assembled battery 10 is equipped with a thermistor 40 that detects the battery temperature of the lithium ion secondary battery 100. The thermistor 40 is electrically connected to the microcomputer 30. Thereby, the microcomputer 30 can know the battery temperature of the lithium ion secondary battery 100.
In addition, a cooling device 50 is electrically connected to the assembled battery 10 via a switch 52. By operating the cooling device 50, the lithium ion secondary battery 100 constituting the assembled battery 10 can be cooled.

  The microcomputer 30 determines whether or not the lithium ion secondary battery is in a dormant state based on the current value I detected by the current detection means 60. Specifically, when the current value I is 1 mA or less, it is determined that the lithium ion secondary battery is in a resting state.

  Further, when it is determined that the lithium ion secondary battery is in the resting state, the microcomputer 30 knows the battery temperature of the lithium ion secondary battery 100 as described above. Then, it is determined whether or not the battery temperature of the obtained lithium ion secondary battery 100 has increased to the first specified value (36 ° C. in the present embodiment).

  Furthermore, when the microcomputer 30 determines that the battery temperature of the lithium ion secondary battery 100 has increased to the first specified value (36 ° C. in the present embodiment), the microcomputer 30 starts cooling the lithium ion secondary battery 100. Control. Specifically, an electrical signal for turning on the switch 52 (see FIG. 2) is transmitted. Thereby, since electric power is supplied from the assembled battery 10 to the cooling device 50, the cooling device 50 operates and the lithium ion secondary battery 100 constituting the assembled battery 10 can be cooled.

  Furthermore, after starting the cooling of the lithium ion secondary battery 100, the microcomputer 30 knows the battery temperature of the lithium ion secondary battery 100. Then, it is determined whether or not the battery temperature of the obtained lithium ion secondary battery 100 has decreased to the second specified value (30 ° C. in the present embodiment). When it is determined that the battery temperature of the lithium ion secondary battery 100 has not decreased to the second specified value (30 ° C. in the present embodiment), the cooling of the lithium ion secondary battery 100 by the cooling device 50 is continued.

  On the other hand, when it is determined that the battery temperature of the lithium ion secondary battery 100 has decreased to the second specified value (30 ° C. in the present embodiment), control to end the cooling of the lithium ion secondary battery 100 is performed. Specifically, an electrical signal for setting the switch 52 to the “OFF” state is transmitted. Thereby, since the power supply from the assembled battery 10 to the cooling device 50 is interrupted, the cooling device 50 can be stopped.

  Thus, the temperature of the lithium ion secondary battery 100 can be kept at a predetermined upper limit temperature value (40 ° C. in the present embodiment) or less during a pause period in which the lithium ion secondary battery 100 is in a pause state. Thereby, an increase in the internal resistance of the lithium ion secondary battery 100 can be suppressed during the suspension period.

By the way, in this embodiment, the lithium ion secondary battery 100 which is a temperature control object is used as the operation power source of the microcomputer 30, the thermistor 40, and the cooling device 50 (see FIG. 2). For this reason, it is not necessary to provide a separate power supply for operation, and the space is saved and the cost is low.
In the present embodiment, the microcomputer 30 corresponds to a temperature control unit.

  As shown in FIG. 3, the lithium ion secondary battery 100 is a rectangular sealed lithium ion secondary battery including a rectangular parallelepiped battery case 110, a positive electrode terminal 120, and a negative electrode terminal 130. Among these, the battery case 110 is made of metal, and includes a rectangular housing portion 111 that forms a rectangular parallelepiped housing space, and a metal lid portion 112. An electrode body 150, a non-aqueous electrolyte 140, and the like are accommodated in the battery case 110 (rectangular accommodation part 111).

  As shown in FIG. 4, the electrode body 150 has an oval cross section, and as shown in FIG. 5, a flat-type winding formed by winding a sheet-like positive electrode plate 155, a negative electrode plate 156, and a separator 157. Is the body. The electrode body 150 is positioned at one end (right end in FIG. 3) in the axial direction (left and right direction in FIG. 3), and a positive electrode winding portion 155b in which only a part of the positive electrode plate 155 overlaps in a spiral shape, Located at the other end (left end in FIG. 3), only a part of the negative electrode plate 156 has a negative electrode winding part 156b that overlaps in a spiral shape. The positive electrode plate 155 is coated with a positive electrode mixture 152 including a positive electrode active material 153 at a portion other than the positive electrode winding portion 155b (see FIG. 5). Similarly, a negative electrode mixture 159 including a negative electrode active material 154 is applied to the negative electrode plate 156 at portions other than the negative electrode winding portion 156b (see FIG. 5). The positive electrode winding part 155 b is electrically connected to the positive electrode terminal 120 through the positive electrode current collecting member 122. The negative electrode winding part 156 b is electrically connected to the negative electrode terminal 130 through the negative electrode current collecting member 132.

In the lithium ion secondary battery 100, lithium nickelate is used as the positive electrode active material 153. In addition, a natural graphite-based carbon material is used as the negative electrode active material 154. Further, as the nonaqueous electrolyte solution 140, non-aqueous electrolyte obtained by dissolving lithium hexafluorophosphate (LiPF ₆ ) in a nonaqueous solvent obtained by mixing EC (ethylene carbonate), DMC (dimethyl carbonate), and EMC (ethyl methyl carbonate). A water electrolyte is used.
The theoretical electric capacity of the lithium ion secondary battery 100 is about 5 Ah.

  Here, the result of investigating the relationship between the battery temperature of the lithium ion secondary battery 100 and the change in the internal resistance (IV resistance) during the pause period will be described in which the lithium ion secondary battery 100 is put into a pause state for 10 hours.

  Specifically, first, three lithium ion secondary batteries 100 (these are referred to as sample batteries A, B, and C) were prepared, and IV resistance values of the respective batteries were measured. Specifically, first, SOC (State Of Charge) was adjusted to 50% for each of the sample batteries A, B, and C in which the battery temperature was maintained at −30 ° C. Thereafter, while maintaining the battery temperature at −30 ° C., each battery was discharged at each current value of 2C, 5C, and 10C, and the battery voltage after 5 seconds from the start of discharge was measured. Thereafter, each measured value is plotted on a graph in which the current value is set on the horizontal axis and the battery voltage is set on the vertical axis. Next, with respect to each of the sample batteries A, B, and C, the slope of a straight line corresponding to the plotted data is calculated using the least square method, and the calculated slope is calculated as the IV resistance value R1 (mΩ before the suspension period). ).

  Thereafter, the sample batteries A, B, and C were maintained in a resting state (a state in which charging / discharging was not performed) for 10 hours while maintaining the battery temperature at −30 ° C. Thereafter, as described above, the IV resistance value R2 (mΩ) after the rest period was obtained for each battery. And about the sample batteries A, B, and C, respectively, the IV resistance value R1 before an idle period was subtracted from the IV resistance value R2 after an idle period, and the difference value (R2-R1) was obtained. This difference value was defined as an internal resistance increase ΔR (= R2−R1) during the rest period when the battery temperature was −30 ° C.

  Further, with respect to the sample battery A, the internal resistance increase ΔR (mΩ) during the pause period was obtained as described above while maintaining the battery temperature at 0 ° C., 25 ° C., and 60 ° C., respectively. . Further, with respect to the sample battery B, the internal resistance increase ΔR (mΩ) during the rest period as described above with the battery temperature maintained at 0 ° C., 25 ° C., 45 ° C., and 60 ° C., respectively. Acquired. Further, with respect to the sample battery C, the internal resistance increase ΔR (mΩ) during the suspension period was obtained as described above with the battery temperature maintained at 0 ° C., 25 ° C., and 60 ° C., respectively. . These results are shown in FIG.

  As shown in FIG. 6, in the lithium ion secondary battery 100, if the resting state (the state where charging / discharging is not performed) continues for a long period (10 hours in the present embodiment), the internal resistance increases. The increase in internal resistance during the suspension period tends to increase as the battery temperature during the suspension period increases. Specifically, when the lithium ion secondary battery 100 has its own temperature higher than 40 ° C. and remains idle for a long period of time, the internal resistance greatly increases. From this result, it can be said that an increase in the internal resistance of the lithium ion secondary battery can be suppressed during the suspension period, particularly by keeping the temperature of the lithium ion secondary battery 100 at 40 ° C. or lower.

Next, temperature control of the lithium ion secondary battery 100 in the automobile 1 of the present embodiment will be described with reference to FIG.
First, in step S1, it is determined whether or not the lithium ion secondary battery 100 constituting the assembled battery 10 is in a dormant state. In the present embodiment, the microcomputer 30 determines whether or not the current value I detected by the current detection means 60 (see FIG. 2) is 1 mA or less. When the current value I is 1 mA or less, it can be determined that the lithium ion secondary battery 100 is in a resting state. On the other hand, when the current value I is larger than 1 mA, it can be determined that the lithium ion secondary battery 100 is not in a resting state.

  If it is determined in step S1 that the lithium ion secondary battery 100 is not in a dormant state (No), the temperature control process is terminated.

  On the other hand, if it is determined in step S1 that the lithium ion secondary battery 100 is in a resting state (Yes), the process proceeds to step S2, and the lithium ion secondary battery 100 is based on the output signal from the thermistor 40 (see FIG. 2). The temperature of the secondary battery 100 is detected. Then, it progresses to step S3 and it is determined whether the battery temperature of the detected lithium ion secondary battery 100 is rising to the 1st specified value (36 degreeC in this embodiment).

  If it is determined in step S3 that the battery temperature of the lithium ion secondary battery 100 has not increased to the first specified value (36 ° C. in the present embodiment) (No), the process returns to step S1 again. The above-described processing is performed.

  On the other hand, if it is determined in step S3 that the battery temperature of the lithium ion secondary battery 100 has increased to the first specified value (36 ° C. in the present embodiment) (Yes), the process proceeds to step S4. Then, cooling of the lithium ion secondary battery 100 constituting the assembled battery 10 is started. Specifically, by setting the switch 52 (see FIG. 2) to the “ON” state, electric power is supplied from the assembled battery 10 to the cooling device 50 and the cooling device 50 is operated. Thereby, the lithium ion secondary battery 100 which comprises the assembled battery 10 can be cooled.

  Next, it progresses to step S5 and the temperature of the lithium ion secondary battery 100 is detected. Then, it progresses to step S6 and it is determined whether the battery temperature of the detected lithium ion secondary battery 100 has fallen to the 2nd regulation value (this embodiment 30 degreeC).

  In step S6, when it is determined that the battery temperature of the lithium ion secondary battery 100 has not decreased to the second specified value (36 ° C. in the present embodiment) (No), the process returns to step S5 again. The temperature of the lithium ion secondary battery 100 is detected.

  Thereafter, if it is determined in step S6 that the battery temperature of the lithium ion secondary battery 100 has been reduced to the second specified value (30 ° C. in the present embodiment) (Yes), the process proceeds to step S7. Then, the cooling of the lithium ion secondary battery 100 (the assembled battery 10) is terminated. Specifically, by setting the switch 52 to the “OFF” state, the power supply from the assembled battery 10 to the cooling device 50 is interrupted, and the operation of the cooling device 50 is stopped.

  Thus, in the present embodiment, the temperature of the lithium ion secondary battery 100 can be kept at 40 ° C. or lower during the pause period in which the lithium ion secondary battery 100 is in a pause state. Thereby, an increase in the internal resistance of the lithium ion secondary battery 100 can be suppressed during the suspension period.

  In the above, the present invention has been described with reference to the embodiments. However, the present invention is not limited to the above embodiments, and it is needless to say that the present invention can be appropriately modified and applied without departing from the gist thereof.

1 is a schematic view of an automobile 1 according to an embodiment. It is the schematic of the battery system 6 concerning embodiment. 1 is a cross-sectional view of a lithium ion secondary battery 100. FIG. 3 is a cross-sectional view of an electrode body 150 of the lithium ion secondary battery 100. FIG. FIG. 5 is a partially enlarged cross-sectional view of the electrode body 150, and corresponds to an enlarged view of a portion B in FIG. FIG. 3 is a diagram showing a relationship between battery temperature and an increase in internal resistance during a rest period of the lithium ion secondary battery 100. It is a flowchart which shows the flow of the temperature control of the lithium ion secondary battery concerning embodiment.

Explanation of symbols

1 automobile 6 battery system 10 assembled battery 30 microcomputer (temperature control means)
50 Cooling device 60 Current detection means 100 Lithium ion secondary battery

Claims (5)

A lithium ion secondary battery;
A temperature control means for controlling the temperature of the lithium ion secondary battery, and a battery system comprising:
The temperature control means includes
A battery system that performs control to keep the temperature of the lithium ion secondary battery below a predetermined upper limit temperature value during a pause period in which the lithium ion secondary battery is in a pause state. The battery system according to claim 1,
The battery system wherein the predetermined upper limit temperature value is 40 ° C. The battery system according to claim 1 or 2,
The temperature control means includes
The battery system which performs control which starts cooling of the said lithium ion secondary battery, when the temperature of the said lithium ion secondary battery reaches the 1st specified value lower than the said upper limit temperature value. It is a battery system as described in any one of Claims 1-3,
A battery system in which the lithium ion secondary battery is used as a power source for operating the temperature control means. An automobile comprising the battery system according to any one of claims 1 to 4,
An automobile in which the lithium ion secondary battery is used as a power source for driving the automobile.

Images